/**
 * 农历转换工具
 * 支持公历日期转农历日期（返回格式如"廿一"）
 */

// 农历数据（1900-2100年）
const lunarInfo = [
    0x04bd8, 0x04ae0, 0x0a570, 0x054d5, 0x0d260, 0x0d950, 0x16554, 0x056a0, 0x09ad0, 0x055d2,
    0x04ae0, 0x0a5b6, 0x0a4d0, 0x0d250, 0x1d255, 0x0b540, 0x0d6a0, 0x0ada2, 0x095b0, 0x14977,
    0x04970, 0x0a4b0, 0x0b4b5, 0x06a50, 0x06d40, 0x1ab54, 0x02b60, 0x09570, 0x052f2, 0x04970,
    0x06566, 0x0d4a0, 0x0ea50, 0x06e95, 0x05ad0, 0x02b60, 0x186e3, 0x092e0, 0x1c8d7, 0x0c950,
    0x0d4a0, 0x1d8a6, 0x0b550, 0x056a0, 0x1a5b4, 0x025d0, 0x092d0, 0x0d2b2, 0x0a950, 0x0b557,
    0x06ca0, 0x0b550, 0x15355, 0x04da0, 0x0a5d0, 0x14573, 0x052d0, 0x0a9a8, 0x0e950, 0x06aa0,
    0x0aea6, 0x0ab50, 0x04b60, 0x0aae4, 0x0a570, 0x05260, 0x0f263, 0x0d950, 0x05b57, 0x056a0,
    0x096d0, 0x04dd5, 0x04ad0, 0x0a4d0, 0x0d4d4, 0x0d250, 0x0d558, 0x0b540, 0x0b5a0, 0x195a6,
    0x095b0, 0x049b0, 0x0a974, 0x0a4b0, 0x0b27a, 0x06a50, 0x06d40, 0x0af46, 0x0ab60, 0x09570,
    0x04af5, 0x04970, 0x064b0, 0x074a3, 0x0ea50, 0x06b58, 0x055c0, 0x0ab60, 0x096d5, 0x092e0,
    0x0c960, 0x0d954, 0x0d4a0, 0x0da50, 0x07552, 0x056a0, 0x0abb7, 0x025d0, 0x092d0, 0x0cab5,
    0x0a950, 0x0b4a0, 0x0baa4, 0x0ad50, 0x055d9, 0x04ba0, 0x0a5b0, 0x15176, 0x052b0, 0x0a930,
    0x07954, 0x06aa0, 0x0ad50, 0x05b52, 0x04b60, 0x0a6e6, 0x0a4e0, 0x0d260, 0x0ea65, 0x0d530,
    0x05aa0, 0x076a3, 0x096d0, 0x04bd7, 0x04ad0, 0x0a4d0, 0x1d0b6, 0x0d250, 0x0d520, 0x0dd45,
    0x0b5a0, 0x056d0, 0x055b2, 0x049b0, 0x0a577, 0x0a4b0, 0x0aa50, 0x1b255, 0x06d20, 0x0ada0,
    0x14b63, 0x09370, 0x049f8, 0x04970, 0x064b0, 0x168a6, 0x0ea50, 0x06b20, 0x1a6c4, 0x0aae0,
    0x0a2e0, 0x0d2e3, 0x0c960, 0x0d557, 0x0d4a0, 0x0da50, 0x05d55, 0x056a0, 0x0a6d0, 0x055d4,
    0x052d0, 0x0a9b8, 0x0a950, 0x0b4a0, 0x0b6a6, 0x0ad50, 0x055a0, 0x0aba4, 0x0a5b0, 0x052b0,
    0x0b273, 0x06930, 0x07337, 0x06aa0, 0x0ad50, 0x14b55, 0x04b60, 0x0a570, 0x054e4, 0x0d160,
    0x0e968, 0x0d520, 0x0daa0, 0x16aa6, 0x056d0, 0x04ae0, 0x0a9d4, 0x0a2d0, 0x0d150, 0x0f252,
    0x0d520
];

// 农历月份名称
const lunarMonthNames = ['正', '二', '三', '四', '五', '六', '七', '八', '九', '十', '冬', '腊'];
// 农历日名称
const lunarDayNames = [
    '初一', '初二', '初三', '初四', '初五', '初六', '初七', '初八', '初九', '初十',
    '十一', '十二', '十三', '十四', '十五', '十六', '十七', '十八', '十九', '二十',
    '廿一', '廿二', '廿三', '廿四', '廿五', '廿六', '廿七', '廿八', '廿九', '三十'
];

/**
 * 公历转农历
 * @param {Date} solarDate 公历日期对象
 * @returns {string} 农历日期字符串（如"廿一"）
 */
export function getLunarDate(solarDate) {
    const year = solarDate.getFullYear();
    const month = solarDate.getMonth() + 1;
    const day = solarDate.getDate();

    // 计算农历日期
    const lunar = solarToLunar(year, month, day);

    // 只返回日部分（如"廿一"）
    return lunarDayNames[lunar.day - 1];
}

/**
 * 公历转农历核心计算
 */
function solarToLunar(y, m, d) {
    // 计算与基准日（1900年1月31日）的天数差
    let offset = daysBetween19000131(y, m, d);

    // 计算农历年份
    let lunarYear = 1900;
    let daysInYear = daysInLunarYear(lunarYear);

    while (offset >= daysInYear) {
        offset -= daysInYear;
        lunarYear++;
        daysInYear = daysInLunarYear(lunarYear);
    }

    // 计算农历月份
    let lunarMonth = 1;
    let leapMonth = leapMonthOfYear(lunarYear);
    let isLeapMonth = false;

    let daysInMonth = daysInLunarMonth(lunarYear, lunarMonth);

    while (offset >= daysInMonth) {
        offset -= daysInMonth;

        // 处理闰月
        if (leapMonth > 0 && lunarMonth === leapMonth && !isLeapMonth) {
            daysInMonth = daysInLunarMonth(lunarYear, lunarMonth, true);
            if (offset >= daysInMonth) {
                offset -= daysInMonth;
                isLeapMonth = true;
            } else {
                break;
            }
        }

        lunarMonth++;
        daysInMonth = daysInLunarMonth(lunarYear, lunarMonth);
    }

    // 农历日（从1开始）
    const lunarDay = offset + 1;

    return {
        year: lunarYear,
        month: lunarMonth,
        day: lunarDay,
        isLeap: isLeapMonth
    };
}

// 辅助函数：计算两个日期的天数差
function daysBetween19000131(y, m, d) {
    // 基准日期：1900年1月31日
    const baseDate = new Date(1900, 0, 31);
    const targetDate = new Date(y, m - 1, d);
    return Math.floor((targetDate - baseDate) / (24 * 60 * 60 * 1000));
}

// 辅助函数：获取农历年份的总天数
function daysInLunarYear(year) {
    let sum = 0;
    for (let i = 1; i <= 12; i++) {
        sum += daysInLunarMonth(year, i);
    }
    if (leapMonthOfYear(year) > 0) {
        sum += daysInLunarMonth(year, leapMonthOfYear(year), true);
    }
    return sum;
}

// 辅助函数：获取农历月份的天数
function daysInLunarMonth(year, month, isLeap) {
    const info = lunarInfo[year - 1900];
    if (isLeap) {
        return (info & 0x10000) ? 30 : 29;
    }
    return (info & (0x10000 >> month)) ? 30 : 29;
}

// 辅助函数：获取农历年份的闰月（0表示无闰月）
function leapMonthOfYear(year) {
    return lunarInfo[year - 1900] & 0xf;
}

export default {
    getLunarDate
};